SQL: Create Multiple Selects Based One Date - sql

Question

I've been searching for help on this but I can't seem to find the solution. What I have is:
Table called Details_Orders.
Columns: CustomerName, InvoiceDate, SaleAmount and SaleCost.
What I want to do is select a date ('1-1-2015') and display the Customer Name, the Date ('1-1-2015'), the sum of SaleAmount for that Date, and the Sum of the SaleCost. And here's the part I'm having problems with, I want the next columns to display the previous months SaleAmount and SaleCost, then the previous YEARS SaleAmount and SaleCost.
I'm having trouble figuring out how to code the Previous Time Periods Select statements. Any help on this would be greatly appreciated.
Select
CustomerName,
InvoiceDate,
Sum(SaleAmount),
Sum(SaleCost),
*PREVIOUS MONTH Sum(SalesAmount) DATEADD(MONTH,-1,'1-1'2015'),
PREVIOUS MONTH Sum(SalesCost) DATEADD(MONTH,-1,'1-1'2015'),
PREVIOUS YEAR Sum(SalesAmount) DATEADD(YEAR,-1,'1-1'2015'),
PREVIOUS YEAR Sum(SalesCost) DATEADD(YEAR,-1,'1-1'2015')*
From Details_Orders
WHERE InvoiceDate='1-1-2015'
Basic

Answer 1

You want to use conditional aggregation, and also need a group by. It is a bit unclear what the exact definitions of previous month and year are. Here is one interpretation:
Select CustomerName,
Sum(case when InvoiceDate = thedate then SaleAmount else 0 end),
Sum(case when InvoiceDate = thedate then SaleCost else 0 end),
Sum(case when year(InvoiceDate)*12 + month(InvoiceDate) =
year(thedate)*12 + month(thedate) - 1
then SaleAmount else 0
end),
Sum(case when year(InvoiceDate)*12 + month(InvoiceDate) =
year(thedate)*12 + month(thedate) - 1
then SaleCost else 0
end),
Sum(case when InvoiceDate < thedate and
InvoiceDate >= dateadd(year, -1, thedate
then SaleAmount else 0
end),
Sum(case when InvoiceDate < thedate and
InvoiceDate >= dateadd(year, -1, thedate
then SaleCost else 0
end)
From (select cast('2015-01-01' as date) as thedate
) params cross join
Details_Orders o
group by CustomerName;